biological rhythms

• Ultradian rhythm 



  A type of biological rhythm which are shorter than a day, eg. stages of sleep.
• Circadian rhythms 



  A type of biological rhythm, subject to a 24 hour cycle which regulates a number of body processes, eg. sleep/wake cycle & changes in core body temperature.
• Infradian rhythm



  A type of biological rhythm which lasts longer than a day, eg. menstruation cycle, & seasonal affective disorder (SAD)
• Endogenous pacemakers



  Internal body clocks that regulate many of our biological rhythms, eg. the influence of the suprachiasmatic (SCN) on the sleep/wake cycle.
• Exogenous zeitgeber


  External cues that may affect our biological rhythms, eg. the influence of light on our sleep/wake cycle.
• Main endogenous pacemaker



  Near the pituitary gland - neurons project from the SCN into the pineal gland
• Superchiasmatic nucleus (SCN) as main endogenous pacemaker

  Ralph et al: removed SCN from a sample of mutant hamsters who had 20 hour sleep/wake cycle & transplanted them into the brains of non-mutant hamsters who has 24 hour sleep/wake cycle. Non mutant hamsters changed to 20 hour cycle of mutant hamsters - shows SCN is dominant endogenous pacemaker.
• Miles: Circadian rhythms - endogenous pacemakers


  A blind man with bodily rhythm near 25 hours suggests we have circadian rhythms governed by internal factors, external cue, eg. light couldn't influence his sleep/wake circadian rhythm
• Luce & Segal: Circadian rhythms - endogenous pacemakers

  People in the Arctic Circle sleep for about 7 hours per night, even in the winter months when there is no sunlight for weeks on end, shows majority of people can still regulate their sleep/wake cycle when there's no sunlight & supports the role of the SCN.
• Aschoff & Wever: Circadian rhythms - exogenous zeitgebers


  Group of ppts spend 4 weeks in a WW2 bunker with no natural light, all but one displayed a circadian rhythm between 24-25 hours, suggests the 'natural' sleep/wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with our 24 hour day.
• Czeisler: Circadian rhythms - exogenous zeitgebers



  Supports exogenous zeitgebers influencing the circadian sleep wake/cycle, could adjust ppts' circadian rhythm from 22 hours to 28 hours.
• Impacts of night shifts & impact on economy


  Shift work disrupts entrainment (in sync with bodily rhythm with external environment) - leads to health problems. More mistakes are made at night in hospitals - more lawsuits. Shift workers more likely to be off ill.
• Advice to new parents trying to get a baby into a normal 24 hour sleep pattern



  Baby should sleep in the dark at night with black out curtains. Baby shouldn't sleep in black out conditions during the day.
• Different stages of sleep- Ultradian rhythm


  Sleep onset, Late night stage, Pre-deep sleep, Deep sleep, REM
• Sleep onset- Ultradian rhythm



  Light sleep can be woken easily, muscles less active - can twitch suddenly, slower eye movement, go through Alpha & Theta brainwaves.
• Late night stage - Ultradian rhythm



  Brainwaves are slower, mainly Theta brain waves, eye movement stops, burst of brain activities, body temp starts to drop, heart rate slows.
• Pre-Deep sleep - Ultradian rhythm



  Slow delta waves, stage between light & deep sleep, hard to be woken up.
• Deep sleep - Ultradian rhythm



  Mostly slow delta waves, hard to be woken up, no eye movement, can experience sleep walking/night terrors in this stage.
• REM 
- Ultradian rhythm



  Rapid Eye Movement. Dreaming occurs. Usually have 2hrs of REM a night. Rapid shallow & irregular breathing. Muscles are paralysed. Hard to wake.
• Dement & Kleitman - Sleep stages (Ultradian rhythm)

  Connected to an EEG at bedtime which took measurements all night, all ppts had periods of REM each night, ppts could recall dreams when awakened during REM, ppts were less likely to report on having a dream when awakened during other stages of sleep, brain activity was different for very vivid dreams, ppts showed different types of REM during REM sleep, the majority of people dream during REM stage of sleep.
• Main functions of sleep


  Survival, essential for brain chemistry, essential for learning.
• Endogenous control on the menstrual cycle - Infradian rhythms 


  Hormones: oestrogen & progesterone. Contraception
• Exogenous zeitgerbers on the menstrual cycle: Infradian rhythms


  Pheromones given off by other women
• Mclintock & Stern: Menstrual cycle - infradian rhythm



  10yr longitudinal study. 29 women: irregular periods. Sweat samples taken from 9 of the women's armpits were dabbed on the upper lips of the other 20. On 68% of occasions it had an effect. If dabbed on top lip in early stage of cycle, it made their cycle longer.
• Issues with Mclintock & Stern 


  Lots of extraneous variables can have an effect. It lack internal validity. Small sample pool. Lack mundane realism: in reality pheromones are more subtle.
• Seasonal effective disorder - Infradian rhythm


  Depression during winter months in northern hemisphere , due to low levels of light: high melatonin, low serotonin.
• Terman: Seasonal effective disorder - Infradian rhythm



  SAD was 5x more common in New Hampshire than in Florida.
• Terman: Seasonal effective disorder - Infradian rhythm



  124 ppts: 85 given 20 minute exposure to bright light, some in the morning & some in the evening, 39 were exposed to negative ions - 60% of am bright light group showed significant improvement, compared to 30% in the evening, only 5% of placebo group showed improvement.